Hood design-Week 2

AUTOMOTIVE HOOD DESIGN

Here we are going to understand and design the concept of the front-mounted engine’s hood according to the standards. The hood or bonnet is the hinged cover over the engine of motor vehicles that allows access to the engine compartment, or trunk for maintenance and repair.

On front-mounted engine cars, the hood may be hinged at either the front or the rear edge, or in the earlier models, it may be split into two sections, on each side, each hinged along the centerline. A further variant combines the bonnet and wheel arches into one section and allows the entire front bodywork to tilt forward and pivot near the front of the vehicle.

Understanding

Hood, which also goes by the term bonnet, mostly in the commonwealth countries, is essentially a type of door that covers the powertrain and other vehicle propulsion system components such as drive belts, battery, fluid levels and lamp unit in the frontal region of an automobile, aside from being a hinged cover the engine, it acts as a critical safety component both for vehicle occupant as well as the pedestrian.

Hood may come with several sub-components, but the two most important ones are the outer panel and inner panels. The inner Panel serves as a structure for the vehicle to dissipate and channel shock waves in the event of a crash while the outer panel serves more as an aesthetic for the automobile’s overall presentation and to channel airflow over the vehicle. Hence, both require critical precision as well as a dedicated strategy right from the design conceptualization to the production step. The initial design goes through iterative design modification based on structural analysis such as fatigue analysis crash analysis.

Before we dive into the design, let us understand the rules and regulation standards for designing the hood.

• A perfect hood design means it should have a great impact distribution angled outside the car.
• In Japan and Europe, regulations have come into effect that places a limit on the severity of pedestrian head injury when struck by a motor vehicle. This is leading to a more advanced hood design, as evidenced by multicore hood inner panel designs.
• European Enhanced Vehicle-Safety Committee (EEVC), European New Car Assessment Program (Euro NCAP).

Pedestrian-Vehicle Collision

• India, however, ranks 1^st in the number of road accident deaths across the 199 countries reported in the World Road Statistics, 2018 followed by China and the US, as per the WHO Global Report on Road Safety 2018, India accounts for almost 11% of the accident-related deaths in the world.
• Road transport remains the most favoured mode of transport for both freight and passenger movement in India. The fast-growing urbanization has made people vulnerable to frequent road accidents resulting in fatalities, injuries/disabilities.
• The sequence of injuries and events in pedestrian collision images are mentioned.

Hood Thickness Information

• Outer Panel Thickness = 0.75mm
• Inner Panel Thickness = 0.75mm
• Reinforcement Thickness = 1.5mm

The process involved in the design of the hoods a sheet metal is:

• Blanking
• Hemming
• Punch Cutting or Piercing
• Deep Drawing
• Embossing

Design of Hood

• Inner Panel Design

• The hood inner panel is required to have a high initial reaction force against the impact exerted on the hood to enhance the energy absorption capacity. The hood is further required to minimize a reduction of a reaction force by deformation in a collision.
• It is an object of the present invention to provide a hood inner panel capable of reduction of a reaction force of the hood inner panel even if a level of deformation of a hood of a vehicle increases, and ensuring a sufficient energy absorption capacity.
• In the inner panel only, we can research and implement the safety of
• pedestrians and as well as the driver. in this panel only we can attach the
• reinforcement, embossed, mastic points, etc.

• Embossing in Sheet Metals

• The metal sheet embossing operation is commonly accomplished with a combination of heat and pressure on the sheet metal, depending on what type of embossing is required. Theoretically, with any of these procedures, the metal thickness is changed in its composition.
• A metal sheet is drawn through the male and female roller dies, producing a pattern or design on the metal sheet. Depending on the roller dies used, different patterns can be produced on the metal sheet. The pressure and a combination of heat actually "irons" while raising the level of the image higher than the substrate to make it smooth. The term "impressing" refers to an image lowered into the surface of a material, in distinction to an image raised out of the surface of a material.

• Deep Drawing

• Deep drawing is a manufacturing process that is used extensively in the forming of sheet metal io a cup or box-like structures. Pots and pans for cooking, containers, sinks, automobile parts, such as panels and gas tanks, are among a few of the items manufactured by sheet metal deep drawing.
• A deep drawing of sheet metal is performed with a punch and die. The punch is the desired shape of the base of the part, once drawn. The die cavity matches the punch and is a little wider to allow for its passage, as well as clearance. For many calculations, the sheet metal thickness is assumed to remain constant. However, there are changes in thickness in certain areas, due to the forces involved.

• Hemming in Sheet Metals

• Hemming is a sheet metal forming process in which sheets are joined by bending it usually to 180°. Automotive body panels and automotive parts such as deck-lids, trunk-lids, doors, hoods, and tailgates are formed by hemming processes.
• Conventional die hemming is suitable for mass production. In die hemming, the flange is folded over the entire length with a hemming tool. Normally the actual hemming is a result informing operation in which the flange is formed with a hemming tool after the drawing and trimming operations have been completed.
• Roll hemming is carried out incrementally with a hemming roller. An industrial robot guides the hemming roller and forms the flange. Roll hemming operation can also be divided into several pre-hemming and final hemming process steps.
• If weld or bolts were used to join the hood panels then the design and the aerodynamic features would get damaged so hemming is more significant to use.
• While doing the hemming process, A relief angle is formed as a product of hem when attaining at the corner of the sheet metals.

• Mastic Data

• They can provide thermal and acoustical insulation, and may serve as fire barriers. They may have electrical properties, as well Sealants can also be used for simple smoothing or filling. They are often called upon to perform several of these functions at once.
• A sealant has three basic functions: It fills a gap between two or more substrates; it forms a barrier through the physical properties of the sealant itself and by adhesion to the substrate; and, it maintains sealing properties for the expected lifetime, service conditions, and environments. The sealant performs these functions by way of correct formulation to achieve specific application and performance properties.

• Hood Components

1. Latch

• A hood latch is a very simple component. It's basically the fastener that keeps your hood closed shut. This latch ensures that your hood is securely connected to your vehicle and that it doesn't pop open unexpectedly.
• When tension is applied to the cable from the hood release handle, it pivots the secondary latch, which pulls away from a retaining seat located under the hood. By design, the secondary latch then releases the hood a few inches before a safety latch takes over.

2. A hinge is a component that fixes the hood to the fenders of the car. The latch is fixed perpendicular to the hinge axis so that the hood opens or closes properly.

3. Latch trajectory motion

• While opening or closing the hood, the latch must be perfectly aligned to the fixing or striker point. For that, the latches trajectory must be perpendicular to the hinge axis.

4. Impact Force Distribution in Hood Design

• A hood design must be made in such a way that when a force is impacted in the front of the hood, all the force must be directed outwards from the vehicle. And the distribution of the force must be controlled along with the hood.

5. Draft Analysis

• 5 degrees of draft analysis is made to the inner panel to find any negative draft, this process is done because we need to develop and submit a positive design to the manufacturers.
• We can see that there are no negative drafts by the inner panel, hence the design is positive and ready to be manufactured.

6. Hood Design